1. Field of the Invention
The present invention relates to a diamond-coated hard metal member exhibiting excellent peeling resistance and good adhesion. More particularly, the present invention relates to a diamond-coated hard metal member that can be used as a cutting tool, such as a milling machine, a single point tool, an end mill, a cutter or a drill, or to a diamond-coated hard member such as an abrasion-resistant member.
2. Description of the Related Art
If a WC-based hard metal substrate is coated with a diamond coat layer, the diamond coat layer can easily peel off the substrate because the two components have largely different thermal expansion coefficients or do not chemically bind to one another. As a countermeasure for preventing peeling of the diamond coat layer, an anchoring effect resulting from a fine roughness formed on the substrate surface has been known to be effective in enhancing the adhesion between the substrate and the diamond coat layer. In particular, a useful technique comprises electrolytically etching the surface of the substrate in such a manner that the surface can be uniformly roughened without significantly damaging the substrate, regardless of the shape of the substrate, and then coating the roughened surface with a diamond coat layer. Extensive studies of this type of technique have been made in an attempt to obtain better adhesion between the substrate and the diamond coat layer.
(1) Processes for controlling the degree of roughness formed on the substrate according to electrolytic etching conditions include the following: (a) a technique employing a specific electrolytic solution, as disclosed in JP-A-03-107460 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-03-146663; (b) a technique of predetermining the etching rate, as disclosed in JP-A-09-020590; and (c) a technique of predetermining a process for applying voltage, as disclosed in JP-A-03-183774.
(2) A technique involving predetermining the hard metal to be electrolytically etched as a starting material, as disclosed in JP-A-04-221075.
(3) A technique of embedding a component as a projection from the surface of a hard metal substrate to be coated with a diamond coat layer, as disclosed in JP-A-08-092741.
However, the foregoing related techniques do not result in sufficient peeling-resistance of the diamond coat layer formed on the roughened surface of the hard metal substrate.
A related technique for controlling the roughness comprises predetermining the electrolytic solution or treatment conditions such that a surface roughness having a sufficient anchoring effect can be formed, without impairing the shape of the WC-based hard metal substrate (e.g., without rendering the blade dull). However, this technique may not result in a surface roughness that can withstand heavy-duty cutting.
In order to form a surface roughness, having a good anchoring effect, on a hard metal substrate, there has been disclosed a method involving the use of a disperse phase component having a high aspect ratio as a hard metal substrate material. There has also been disclosed a method of attaching to the surface of a hard metal substrate a particulate component which, after electrolytic etching, remains projecting from the substrate. However, neither of these two methods can sufficiently achieve the desired result.
An object of the present invention is to solve the foregoing problems of the related art.
It is a further object of the present invention to provide a diamond-coated hard metal member having excellent abrasion resistance and adhesiveness good enough to withstand an impact resulting when the element is used as a cutting tool for heavy-duty cutting, such as the milling of an aluminum alloy.
In accordance with the first aspect of the present invention, there is provided a diamond-coated hard metal member comprising a hard metal substrate having a roughened surface and a diamond coat layer coating the roughened surface, either directly or with an interlayer interposed therebetween. The interlayer contains a metal or compound thereof, coats the substrate, has a roughened surface corresponding to the roughened surface of the substrate, and has fine projections having an average longest diameter of not more than 3.2 xcexcm at the base thereof in a density as high as not less than 0.08/xcexcm2.
In accordance with the second aspect of the present invention, there is provided a diamond-coated hard metal member comprising a hard metal substrate having a roughened surface and a diamond coat layer coating the roughened surface, either directly or with an interlayer interposed therebetween. The interlayer contains a metal or compound thereof, coats the substrate, and has a roughened surface corresponding to the roughened surface of the substrate, which is obtained by electrolytically etching a WC-based hard metal substrate comprising WC as a main component. The unetched substrate contains a metal element or compound thereof, and comprises a disperse phase having a sufficiently lower electrolytic etching rate than WC dispersed therein in a surface region to at least a thickness that can be electrolytically etched in an amount of from 2 to 5 mol-% as calculated in terms of the metal element. The surface of the unetched substrate has small diameter disperse phases having an average longest diameter of from not less than 0.5 xcexcm to less than 2 xcexcm in a density of from not less than 0.1/xcexcm2 to not more than 0.2/xcexcm2, or large diameter disperse phases having an average longest diameter of from not less than 2 xcexcm to not more than 3 xcexcm in a density of from not less than 0.03/xcexcm2 to not more than 0.1/xcexcm2.
The second aspect of the present invention can further include the roughened surface of the substrate having fine projections having an average longest diameter of not more than 3.2 xcexcm at the base thereof in a density as high as not less than 0.08/xcexcm2.
The disperse phase can contain at least one metal element selected from the group consisting of elements belonging to the Groups IVa, Va and VIa (excluding W) of the periodic table of elements, or a compound thereof.
The reason why the foregoing related art cannot necessarily provide a roughened surface that can sufficiently withstand heavy-duty cutting under some electrolytic etching conditions for controlling the form of surface roughness of hard metal substrate will now be described.
Electrolytic etching makes the use of the difference in electrical solubility between the components constituting a hard metal substrate. In the case of a WC-based hard metal substrate for example, a roughened surface is formed with disperse phases as projections because disperse phase components are electrolytically etched away at a remarkably lower rate than WC and binding phase (xcex3-phase) components (one or more of Co and Ni). Therefore, the number and size of projections on the roughened surface formed by electrolytic etching depend not only on the electrolytic etching conditions, but also on the surface structure of the hard metal substrate. In the related art, the surface structure of an unetched hard metal substrate to which a diamond layer can be sufficiently attached has not been definitely disclosed.
The inventors focused on the fact that the form of roughness on the surface of an electrolytically etched hard metal substrate depends on the content of disperse phase in the surface layer region (at least to a depth that can be electrolytically etched) of unetched hard metal substrate, and also on the size and density of disperse phases on the surface of the substrate. These factors thus have a great effect on the adhesion of the diamond coat layer. The inventors conducted electrolytic etching of a hard metal substrate, the surface layer region of which has a predetermined composition and structure at least to a depth that can be electrolytically etched, and then formed a diamond layer on the roughened surface of the hard metal substrate. It was found that the diamond layer thus formed has an adhesion good enough to withstand impact developed when the element is used as a cutting tool for heavy-duty cutting, such as milling of aluminum alloy.
The numerical range as used herein contains not only both extreme values, but also all arbitrary intermediate values contained therein, unless specifically stated otherwise.
The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.